Lubricants



Sept 14, 1948. B. P. ROBERTSON i 2,449,510

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/Vormal Press are wnmsssss: INVENTOR Patentedy Sept. 14,1948

Billy P. Robertson, Pittsburgh, Pa.,

Westinghouse Electric Corporation,

assignor to East Pittsburgh, Pa., a corporation of Pennsylvania appuesuon May '1, 194s, serial No. 607,173

claims. (ci. 25a-49.1)

This invention relatesto novel lubricant cornpositions.v The compositions are characterized by ability to vwithstand high temperatures and excellent anti-friction properties at extreme pressures.

There have been disclosed to the art a number of fluid compositions consisting essential yy of f organo-silicon oxide polymers, commonly known as silicones, having the unit formula:

iii-1 where R1 and Rzk are alkyl radicals and .is greater than 3. Both R1 andRz may consist of such alkyl groups as methyl, ethyl, propyl, isopropyl, butyl and amyl. The fluids may have viscosities of from less than 50 centistoires to 5000' centi- .Stokes-and higher. The most useful fluids for the purpose of this invention are those in which :c has a value each molecule of the polymer may be either trialkyi silicon groups or dialkyl silicon hydroxyl groups. However, in some cases, the polymers are believed to consist of rings in which no terminal groups are present. In any event, itis undesirable to have any significant amount of monoalkyl silicon groups present, since such groups tend to cause cross-linking and result in resinous or solid materials being produced. The best results for the purpose of this invention have been obtained with compositions in which dimethyl silicone fluids are employed. While the dialkyl silicon oxide polymeric fluid-s have many unusual characteristics, such, for example, as an extremely flat temperature-viscosity curve, they have been found to be unsatisfactory as lubricants due to a lack of nlm strength and anti-friction values as low as those possessed by ordinary petroleum lubricants. The purpose of this invention is to produce useful lubricants from such silicone uids.

The object of this invention is to prepare a of or more'. The terminal'groups in' molybdenum. tungsten, and titanium.A ammirnurn amount equal to 0.1% of the weight of the -fluid dialkyl silicone is required to produce the lubricants of this invention. The finely divided solid should be added in an amount equal to from 2% to 10% or more of the weight `of the dialkyl silicone to achieve optimum properties. `'I he compound molybdenum disulphide will be referred to hereinafter specifically as typical of all the other compounds that may be added to the polymeric silicones.

Referring to Figure 1 of the drawing, there is illustrated the values ofthe coefficient of ,friction` under heavy normal pressures for a liquid dimethyl silicone lubricant with molybdenum disulphlde combined therewith. The curve `A was obtained by applying a liquid dimethyl silicone hav-' ing a viscosity of 1000 centistokes toa standard friction-testing machine provided with four halfinch steel balls disposed in a cluster with one of the balls revolving at a speed of 1.8 revolutions per minute with respect to the others. It'will be noted that the coefficient of friction increased as the normal pressure on the balls increased. Furthermore, all the friction values are relatively high under the test conditions. As shown inr curve B, a' composition composed of 50 grams of the same di.- methyl silicone lubricant as employed in determining curve A, combined with 90 grams of eolloidally fine molybdenum disulphide, gave remarkably improved results in the same test machine. The coefllcient of friction is not only relatively uniformybut is of a value which is favorably comparable with that obtained with the 4best petroleum lubricants available to the trade.

The curve C in Fig. 1 of the drawing is that secured by testing a ,grease prepared from a fluid lubricant composition having excellent anti-fric- I tion properties combined with the thermal stability of silicones.

Other objects of the invention will, in part. be obvious, and will, in part. appear hereinafter.V

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description and drawing, in which:

Figures 1 and 2 are graphs.

It has been discovered that fluid dialkyl silicones may be combined with colloidally fine solid compounds selected from the class consisting of the disulphides, selenides. and tellurides of dimethyl silicone combined with silica gefl toform a grease. It will be noted that the improvement by incorporating silica gel is relativelyy meager. Therefore, molybdenum disulphideand other related solid compounds produce an unexpected result by converting a poor lubricant to an excellent lubricant.

Referring to Fig. 2 of the drawing, there are illustrated a plurality of curves obtained by plot` ting shearing stress against pressure for a number of different silicone compositions. The curve D ls that obtained by plotting the shearing stress against pressure obtained by testing a grease composed of dimethyl silicone and colloidal silica equal to approximately 50% of the weight of the dimethyl silicone fluid. The curve D indicates a characteristic of disproportionate increase in bricating applications produce pressures of' the order shown in the graph. The same grease from which the data. of curve D were obtained was combined with 5% colloidally fine molybdenum disulphlde and tested in the same way. The curve E indicates the unusual and marked improvement secured. The lubricating properties of the composition containing the molybdenum disulphlde are satisfactory and would be welcomed by the trade.

In preparing the improved compositions of this invention, the solid material, such as molybdenum disulphlde, if relatively pure and free from abrasives, may be ball milled in the presence of the dialkyl silicone for a period of time of from twenty-four to forty-eight hours, or longer, until a relatively stable suspension is produced. The

suspension may be diluted with more dialkyl` silicone fluid to produce a composition of any desired consistency. For the purpose of this invention, the solids are the highly purified solids prepared in accordance wlththe patent of E. B. Kaercher, No. 2,367,946. The purified molybdenum disulphide and the like produced by the process of that patent is already in a colloidal lstate of division and only a brief ball milling with the dlalkyl silicone is necessary to secure a. rela.- tively permanent suspension. A suspending agent, such as diglycol stearate or gum arabic in an amount equal to 1% of the weight of the molybdenum disulphlde, maybe added in order to maintain the suspension over a prolonged period of storage, though this is not absolutely necessary.

In preparing a grease-like lubricant composition, 100 parts by weight of a polymeric dialkyl silicon oxide fluid is admixed with from to 100 parts by weight of colloidal silica, such as silica gel, and from one-tenth part to a hundred parts by weight of molybdenum disulphlde or other compound. A brief ball milling operation is sufflcient to produce a suitable grease for various applications. l

The oils and greases have been tested at temperatures of as high as 300 F. for prolonged periods of time without any substantial deterioration thereof. The outstanding low coefcient of friction and'other properties have been maintained even after many hours use of the lubricants at such elevated temperatures.

Specific examples of other colloidal solids from the class above mentioned which are useful for converting relatively unsatisfactory silicone fluids to good lubricants are tungsten disulphlde, titanium sulphide, titanium telluride, molybdenum selenide and tungsten selenide.

Since certain obvious changes may be made in the above procedure and different embodiments of the invention could be made Without departing from the scope thereof, it is intended ,that all matter contained in the above description and drawing shall be taken in connection with the accompanying claims and not in a limiting sense.

, 4 I claim as my invention: 1. A lubricant comprising, in combination, a polymeric silicon oxide having the unit formula:

til-rl.

oxide of a finely divided solid compound selected from the class` consisting of the disulphides, se,`\'V

lenides andw tellurides of molybdenum, tungsten,l

and titanium.

2. A lubricant comprising, in combination, a polymeric dimethyl silicon oxide subs-tantially free from monomethyl silicon oxide groups, the

polymeric dimethyl silicon oxide having lubricating characteristics, and from 0.1% to about 180% of the weight of the polymeric silicon oxide of a finely divided solid compound selected from the class consisting of the disulphides, selenidesand tellurides of molybdenum, tungsten, and titanium.

3. A lubricant comprising, in combination, a polymeric dimethyl silicon oxide substantially free from monomethyl silicon oxide groups, the polymeric dimethyl silicon oxide having lubricating characteristics, from 0.1% to about 180% of the Weight of the polymeric silicon oxide of a finely divided solid compound selected from the class consisting of the disulphides, selenides and tellurides of molybdenum, tungsten, and titanium, and a suspending agent for the molybdenum disulphide. r

4. A high temperature grease comprising, in combination, a polymeric silicon oxide having the unit formula:

[sila] i, 4

where Ri and Rz are saturated aliphatic radicals and .1: is greater than 3, the polymeric silicon oxide having oily characteristics, and from 10% to of the weight of the polymeric silicon oxide of silica in colloidal form, and from 0.1% to about of the weight of the polymeric silicon oxide cfa finely divided solid compound selected from the class consisting of the disulphides, selenides and tellurides of molybdenum, tungsten, and titanium.

5. A high temperature grease comprising, in combination, a polymeric dimethyl silicon oxide substantially free from monomethyl silicon oxide groups, the polymeric dimethyl silicon oxide having lubricating/ characteristics, and from 10% to 100% of the weight of the polymeric silicon oxide of silica in colloidal form, and from 0.1% to about 180 of the weight' of the polymeric silicon oxide of a finely divided solid compound selected from the class consisting of the disulphides, selenides and tellurides of molybdenum, tungsten, and titanium.

BILLY P. ROBERTSON. 

